ASM INTERNATIONAL The Materials Information Company ® Publication Information and Contributors Introduction Composites was published in 2001 as Volume 21 of ASM Handbook The Volume was prepared under the direction of the ASM International Handbook Committee Volume Chair Daniel B Miracle and Steven L Donaldson were the Volume Chairs Authors and Contributors • R.C Adams Lockheed Martin Aeronautical Systems • Suresh Advani University of Delaware • David E Alman U.S Department of Energy • Finn Roger Andressen Reichhold AS • Keith B Armstrong Consultant • B Tomas Åstrưm IFP SICOMP AB • Amit Bandyopadhyay Washington State University • Yoseph Bar-Cohen Jet Propulsion Laboratory • Robert J Basso Century Design Inc • Mark Battley Industrial Research Limited • Joseph J Beaman, Jr University of Texas at Austin • John H Belk The Boeing Company • Tia Benson Tolle Air Force Research Laboratory • Barry J Berenberg Caldera Composites • Tom Bitzer Hexcel Corporation • John Bootle XC Associates Inc • Chris Boshers Composite Materials Characterization Inc • Richard H Bossi The Boeing Company • David L Bourell University of Texas at Austin • Dennis Bowles Northrop Grumman Corporation • Jack Boyd CyTech Fiberite Inc • Maureen Boyle Hexcel Corporation • Shari Tidrick Bugaj Fibercote Industries Inc • Frank Burzesi XC Associates Inc • Flake C Campbell The Boeing Company • Karl K Chang DuPont • K.K Chawla University of Alabama • N Chawla Arizona State University • Eric Chesmar United Airlines • Richard J Chester Aeronautical and Maritime Research Laboratory • S Christensen The Boeing Company • William F Cole II United Airlines • Bruce Crawford Deakin University • George Dallas TA Instruments • Joseph R Davis Davis & Associates • J.A DiCarlo NASA Glenn Research Center • Cynthia Powell Doğan U.S Department of Energy • Roderick Don University of Delaware • Steven L Donaldson Air Force Research Laboratory • Louis C Dorworth Abaris Training Resources Inc • Richard Downs-Honey High Modulus New Zealand Limited • T.E Drake Lockheed Martin Aerospace • Lawrence T Drzal Michigan State University • G Ehnert Menzolit-Fibron GmbH • D Emahiser GKN Aerospace • Roger W Engelbart The Boeing Company • Don O Evans Cincinnati Machine • Richard E Fields Lockheed Martin Missiles and Fire Control • Lynda Fiorini XC Associates Inc • Gerald Flanagan Materials Sciences Corporation • Mark S Forte Air Force Research Laboratory • Marvin Foston Lockheed Martin Aeronautical Systems • Luther M Gammon The Boeing Company • C.P Gardiner Defence Science & Technology Organisation, Australia • Nicholas J Gianaris Visteon Corporation • Ian Gibson The University of Hong Kong • Lawrence A Gintert Concurrent Technologies Corporation • John W Goodman Material Technologies Inc • J.H Gosse The Boeing Company • Michael N Grimshaw Cincinnati Machine • Olivier Guillermin Vistagy Inc • H Thomas Hahn Air Force Office of Scientific Research • Paul Hakes High Modulus New Zealand Limited • William C Harrigan MMC Engineering Inc • L.J Hart-Smith The Boeing Company • Brian S Hayes University of Washington • Dirk Heider University of Delaware • Edmund G Henneke II Virginia Polytechnic Institute and State University • John M Henshaw University of Tulsa • G Aaron Henson III Design Alternatives Inc • Rikard B Heslehurst Australian Defence Force Academy • Arlen Hoebergen Centre of Lightweight Structures TUD-TNO • Leslie A Hoeckelman The Boeing Company • Michael J Hoke Abaris Training Resources Inc • J Anders Holmberg SICOMP AB • K Hörsting Menzolit-Fibron GmbH • Warren H Hunt, Jr Aluminum Consultants Group Inc • Michael G Jenkins University of Washington • L Kahn Georgia Institute of Technology • Vistasp M Karbhari University of California, San Diego • Kristen M Kearns Air Force Research Laboratory • Shrikant N Khot University of Delaware • Jeffrey J Kilwin The Boeing Company • Jim Kindinger Hexcel Corporation • Donald A Klosterman University of Dayton • Frank K Ko Drexel University • Greg Kress Delta Air Lines • Lawrence F Kuberski Fischer U.S.A • R Kühfusz Menzolit-Fibron GmbH • Joseph M Kunze Triton Systems • Joe Lautner Gerber Technology Inc • Richard D Lawson The Boeing Company • David Lewis III Naval Research Laboratory • Hong Li PPG Industries Inc • R Liebold Menzolit-Fibron GmbH • Shyh-Shiuh Lih Jet Propulsion Laboratory • Jim R Logsdon EMF Corporation • Peter W Lorraine General Electric Company • Bhaskar S Majumdar New Mexico Institute of Mining and Technology • Ajit K Mal University of California, Los Angeles • Cary Martin Hexcel Corporation • Jeffrey D Martin Martin Pultrusion Group • James J Mazza Air Force Research Laboratory • John E McCarty Composite Structures Consulting • Douglas A McCarville The Boeing Company • Colin McCullough 3M Company • Lee McKague Composites-Consulting Inc • James McKnight The Boeing Company • • J Lowrie McLarty Carol Meyers Materials Sciences Corporation • Andrew Mills Cranfield University • Daniel B Miracle Air Force Research Laboratory • Stephen C Mitchell General Electric Aircraft Engines • John E Moalli Exponent Failure Analysis Associates • Robert Moore Northrop Grumman Corporation • A.P Mouritz RMIT University • John Moylan Delsen Testing Laboratories • Thomas Munns ARINC • John Neuner Fabrics and Preforms Introduction WOVEN MATERIALS, in laminate form, are currently displacing more traditional structural forms primarily because of the availability of fibers (such as carbon and aramid) whose enhanced mechanical properties in composite form surpass the property values of corresponding hardware in aluminum or steel on a strength-toweight basis Woven broad goods, considered to be intermediate forms, present these fibers in a more convenient format for the design engineer, resin coater, and hardware fabricator The many variations of properties made possible by combining different yarns and weaves allow the structural engineer a wide range of laminate properties The designer should understand the operation of weaving hardware and textile design details in order to select the best fabric style This article describes the types of fabrics and preforms that are used in the manufacture of advanced composites and related selection, design, manufacturing, and performance considerations Fabrics and Preforms Unidirectional and Two-Directional Fabrics The fabric pattern, often called the construction, is an x, y coordinate system The y-axis represents warp yarns and is the long axis of the fabric roll (typically 30 to 150 m, or 100 to 500 ft) The x-axis is the fill direction, that is, the roll width (typically 910 to 3050 mm, or 36 to 120 in.) Basic fabric weaves are few in number, but combinations of different types and sizes of yarns with different warp/fill counts allow for hundreds of variations The most common weave construction used for everything from cotton shirts to fiberglass stadium canopies is the plain weave, shown in Fig The essential construction requires only four weaving yarns: two warp and two fill This basic unit is called the pattern repeat Plain weave, which is the most highly interlaced, is therefore the tightest of the basic fabric designs and most resistant to in-plane shear movement Basket weave, a variation of plain weave, has warp and fill yarns that are paired: two up and two down The satin weaves represent a family of constructions with a minimum of interlacing In these, the weft yarns periodically skip, or float, over several warp yarns, as shown in Fig The satin weave repeat is x yarns long and the float length is x–1 yarns; that is, there is only one interlacing point per pattern repeat per yarn The floating yarns that are not being woven into the fabric create considerable looseness or suppleness The satin weave produces a construction with low resistance to shear distortion and is thus easily molded (draped) over compound curves, such as an aircraft wingroot area This is one reason that satin weaves are preferred for many aerospace applications Satin weaves can be produced as standard four-, five-, or eight-harness forms As the number of harnesses increases, so the float lengths and the degree of looseness and sleaziness, making the fabric more difficult to control during handling operations Textile fabrics generally exhibit greater tensile strength in plain weaves This distinction fades in the composites field Fig Plain weave, yarn interlacing Fig Five-harness satin weave, interlacing The ultimate laminate mechanical properties are obtained from unidirectional-style fabric (Fig 3), where the carrier properties essentially vanish in the laminate form The higher the yarn interlacing (for a given-size yarns), the fewer the number of yarns that can be woven per unit length The necessary separation between yarns reduces the number that can be packed together This is the reason for the higher yarn count (yarns/in.) that is possible in unidirectional material and its better physical properties Unidirectional material has the most “unbalanced” weave and is usually reserved for special applications involving hardware with axial symmetry (such as a carbon-fiber-reinforced shuttle motor case) fabricated using a tape-wrapping operation Fig Unidirectional weave A weave construction known as locking leno (Fig 4), which is used only in special areas of the fabric, such as the selvage, is woven on a shuttleless loom The gripping action of the intertwining leno yarns anchors or locks the open selvage edges produced on rapier looms The leno weave helps prevent selvage unraveling during subsequent handling operations, but is unsatisfactory for obtaining good laminate physical properties However, it has found applications where a very open (but stable) weave is desired Fig Full-width plain weave with leno selvage The textile designer is concerned with only a few fabric parameters: type of fiber, type of yarn, weave style, yarn count, and areal weight Standard methods for measuring such parameters are well documented in Ref The verification of quality is an important aspect of the aerospace materials business Quality is usually governed by military specification as part of the purchasing requirements Typical quality defects, such as missing or broken warp or fill yarns, fabric misorientation (pucker), and misweaves in the pattern due to equipment failure or foreign material on the fabric, are documented in Ref and Weave construction is the realm of the textile engineer, but fabric mechanical properties and how they translate into the laminate are concerns of the composite design engineer Maximum directional properties for the minimum material (thickness) are attained with unidirectional-style material The more usual goal of balanced properties requires two-directional styles The fiber obviously dominates those properties carried by the fabric into a structural composite The fiberglass industry has these well-established fabric styles and categories: Fabric weight Areal wt, kg/m2 (oz/yd2) Thickness, μm (mil) Light 0.10–0.35 (3–10) 25–125 (1–5) Intermediate 0.35–0.70 (10–20) 125–250 (5–10) Heavy 0.50–1.0 (15–30) 250–500 (10–20) The newer carbon and aramid fiber industries are somewhat oriented to custom design, but as the aerospace market matures, a few fabric constructions may become standards Table provides a sampling of styles that have found uses, along with corresponding order-of-magnitude epoxy resin composite properties Table Typical fabric styles and composite properties Weave Yarns/in., warp × fill Weight Thickness at 25 kPa (3.4 psi) 2 kg/m oz/yd mm in Typical fabric weaves Eight-harness satin 24 × 23 Eight-harness satin 24 ì 23 12ẵì 12ẵ Plain 0.370 0.370 0.190 10.9 10.9 5.6 0.46 0.48 0.30 0.018 0.019 0.012 0.125 3.7 0.20 0.008 Five-harness satin 24 × 24 24 × 12 0.20 6.0 0.23 0.009 CFS 11ẵì 11ẵ 0.19 5.7 0.25 0.010 Plain 0.370 10.9 0.50 0.020 Five-harness satin 11 × 11 8×8 0.525 15.5 0.81 0.032 Plain 0.755 22.2 1.0 0.040 Eight-harness satin 10ẵì 10ẵ 10 ì 10 0.345 10.2 0.48 0.019 Plain 21 × 21 0.393 11.6 0.38 0.015 8HS Property Value Typical composite properties (balanced weave) 620–690 (90–100) Tensile strength, MPa (ksi) 69–76 (10–11) Tensile modulus, GPa (106 psi) 690–900 (100–130) Flexural strength, MPa (ksi) 62–69 (9–10) Flexural modulus, GPa (10 psi) 620–690 (90–100) Compressive strength, MPa (ksi) Compressive modulus, GPa (10 psi) 62–69 (9–10) Short beam shear strength, kPa (psi) 55–69 (8–10) 1.6 Specific gravity The following data illustrate the relative market importance of various aerospace textile intermediate forms: Woven 90+% Filament winding 5%